Variable resistor



Jan. 20, 1959 E. D. O'BRIAN VARIABLE RESISTOR Filed Dec. 3, 1956 IN V EN TOR.

ilnited States Patent VARIABLE ansrsron Edward D. OBrian, Anaheim, Calif., assignor to Booms Laboratories, Inc.

Application December 3, 1956, Serial No. 625,683

3 Claims. (Cl. 20162) This invention relates to new and improved adjustable electrical instruments such as variable resistors, potentiometers and the like.

Variable resistors and potentiometers are being used more and more frequently for a wide variety of difierent control and other applications. As the use of these instruments increases the demand for better and more inexpensive units is becoming more and more pronounced. A basic object of this invention is to provide electrical instruments such as, for example, potentiometers and variable resistors which arev extremely inexpensive to manufacture. A related object of the invention is to provide units of this category which are specifically designed so that they may be readily built to any number of different stock sizes with a minimum of difiiculty utilizing interchangeable parts between the stock sizes. It is also an object of the present invention to provide adjustable electrical instruments of the indicated variety which are extremely reliable and which are capable of withstanding a great deal of physical abuse.

Because of the nature of this invention it is not considered necessary to set forth in the specification a further long list of objects and advantages of it. Various other objects and advantages of the invention itself will be fully apparent to those skilled in the art to which this invention pertains from a detailed consideration of the remainder of this description including the appended claims and the accompanying drawing in which:

Fig. l is a perspective view of an electrical instrument of this invention;

Fig. 2 is a cross sectional view taken at line 2-2 of Fig. 1;

Fig. 3 is a cross sectional view taken at line 3-3 of Fig. 2;

Figs. 4, S and 6 are perspective views illustrating the construction of certain parts of the instrument illustrated in Fig. l; and i Fig. 7 .is a diagrammatic perspective view indicating a step in the manufacture of the instrument illustrated in Fig. 1'.

in all figures of the drawing like numerals are used to designate like parts. it is to be understood that this invention is not to be limited by the accompanying drawing. In this drawing a presently preferred embodiment of the invention is shown. Obviously those skilled in art to which the invention pertains may design a large number of other differently appearing units which utilize the .essential principles of'this invention.

As an aid to understanding the invention herein involved it may be stated in essentially summary form that this invention involves adjustable electrical instruments, each of which is formed so as to comprise or include an elongated housing within which there are rormed two elongated cavities connected by a passage. Within one of these cavities there is located a resistance element; within the other of these cavities there is located a threaded shaft which extends from housing proper so as to her a head located externally of the housing.

In addition an electrical instrument of this invention includes cap means as will hereinafter be described sealing the ends of the housing and securely holding the shaft and the resistance element employed in position. Also with an electrical instrument of the invention a contact member is positioned within the passage indicated so as to extend into the cavities indicated so as to be engaged by the threaded shaft and so as to engage the resistance element,

The actual nature of this invention is best more fully explained by referring directly to the accompanying drawing. in Pig. 1 there is shown a complete potentiometer iii formed in accordance with this invention so as to include an elongated housing 12. This housing 12 may be conveniently formed to any desired length by various extrusion techniques utilizing any of a wide variety of different thermoplastic materials such as for example certain vinyl compositions. It is preferred to form the housing 12 out of various polyolefins such as polyethylene. By such extrusion techniques the housing 12 may be conveniently formed so as to have a first and second elongated cylindrical cavity 14 and 16 extending between its ends 18 and 20 and so as to include a passage 22 interconnecting these two cavities 14 and 16 the entire distance between the ends 18 and 29. As is best seen in Fig. 3 of the drawing the passage 22 is formed so as to have internal shoulders 24 in such a manner that the portion of passage 22 adjacent to the cavity 14- is of larger width than the portion of the passage 22 adjacent to the cavity 16.

Within the cavity 16 there is provided an elongated cylindrical resistance element 26 of conventional construction consisting of a non-conductive base 28 around which there is located a resistance winding 36. The ends of this resistance winding 30 are directly connected as by welding to wires 32 which extend from the resistance element 30 out around the ends 18 and 29 of the housing 12 as illustrated in Fig. 2. Within the passage 22 there is positioned against the shoulders 24 an electrical return element 34 of metal having side strips 36 connected at its ends by connecting areas 38. As will be seen in Fig. 2 of the drawing these connecting areas 38 are positioned a short distance beyond the ends 13 and 20. The return element 34 is designed so as to be engaged by a small metal contact member 46 formed as illustrated in Fig. 4 of the drawing so as to include a relatively flat center section 42 and upstanding sides 44, the ends of which are serrated at 46 corresponding in shape and dimension to the threads upon a threaded section 48 of a threaded shaft 50. From the center section 42 there extends a small resilient contact finger 52 which normally engages the resistance winding 30 in a known manner. Another wire 32 is connected as by welding to one of the connecting areas 38 so as to extend around an end 20 of the housing 12.

The shaft 50 is provided with a conical end 54 extending beyond the end 20 of the housing 12. This shaft is also provided with a smooth neck portion 56 of reduced diameter extending past the other end 18 of the housing 12 and with a conventional slotted head 58 supported by the neck 56 so as to be spaced from the housing 12. Upon the neck 56 there is located a small flange 60. The ends 18 and 20 of the housing 12 are adapted to be closed by means of caps 62 and 64. These caps are preferably formed of the same material as the housing 12 by conventional molding techniques or are formed of a material which may be readily bonded to the material composing the housing 12 by convenient conventional means such as, for example, heat.

In assembling the potentiometer 10 the caps 62 and 64 are pushed into the positions shown so that various cavities 66 within these caps carry the ends of the reasrrrsos sistance element 26, the electric return element 3d and the conical end 54 of the shaft 56 and the neclc 56 of this shaft 50. As the parts for the potentiometer 1% are being positioned together it is unnecessary to securely attach the caps 62 and 64 to the housing 12. Also it is unnecessary to completely form the cavity 66 containing the flange 66 to the shape of this flange. These operations may be conveniently accomplished as indicated in Fig. 5 of the drawing by pressing against the caps 62 and hot dies 68 serving to seal these caps to the housing 12. The temperature of these dies will vary depending upon the materials used for the caps 62 and 64 and the housing 12 employed; the pressure required will also vary correspondingly. The action of these hot die also creates within the cap 62 a close fit against the flange 66 serving to effectively lock the shaft 559 in the position shown. if the portions of the shaft 56 carried by the caps 62 and 6 1- are treated prior to assembly with an appropriate material such as, for example, a silicone release agent the scaling procedure employed in attaching the caps 62 and 64 will not bond the shaft 56 to these caps and, thus, the shaft 51 may be turned with the final construction shown readily.

This manufacturing procedure is quite advantageous in that what in effect are small flange-like sealing areas closely surrounding the neck 56, the flange 66 and the back of the head 53 of the shaft 56 are created during the final assembly of the caps 62 and 64. Such assembly also provides sealed in lead or terminal structures leading into the return element 34 and the resistance element 26. Thus, the entire potentiometer lid is completely sealed except around the neck 56 of the shaft 5-6. Here sufiicient means are provided so as to form an effective seal against the conditions normally encountered in use.

Those skilled in the art to which this invention pertains will realize that when the housing 12 is formed by extrusion techniques from various thermoplastic resins as indicated that this housing may be readily cut to any desired length and that the caps 62 and 64 shown and described may be utilized with any length of housing. The particular shape of the electrical return element 34 is considered advantageous inasmuch as the side strips 36 provide a bearing surface against which the center section 42 of the contact 46 may bear. Preferably this contact 4-0 is constructed in such a manner of a resilient metal that the grooves 46 resiliently engage the threaded section d3 of the shaft 56.

Those skilled in the art to which this invention pertains will further realize that the potentiometer lltl is a very compact unit which is capable of withstanding a great deal of physical abuse. When the housing 12 and the caps 62 and 64 are formed of the materials indicated these parts of the potentiometer it) are capable of withstanding a great deal of physical abuse. Further, with the precise assembly shown it i virtually impossible to locate the resistance element 26 and the shaft 56 in other than the desired locations during assembly. It is to be specifically noted that the cavity 14 is of a greater than semi-circular cross sectional configuration so as to firmly hold the shaft 56 in position, even during assembly of this instrument and that the cavity 116 is of similar dimeusion.

Obviously a large number of modifications can be made in the construction shown without departing from the essential nature of this invention. As an example of this the potentiometer lltl may be manufactured as a variable resistor by merely omitting one of the wires 32 connected to one end of the resistance winding Also rigid supports may be employed for the housing 32, and the caps 62 and 64 may be similarly constructed of other materials besides those indicated. Insofar as such modifications are within the skill of the art they are to be considered as falling within the scope of the appended claims. Whenever the term means" is employed in these claims it is to be taken as defining the corresponding structure set forth in this specification or the equivalent of the same.

i claim:

'1. A variable resistor comprising, in combination, a housing having an enclosed cavity provided therein, a resistance element mounted on said housing within said cavity, a rotatable leadscrew journaled on said housing and extending through said cavity parallel to said re sistance element, a pair of shoulders on said housing disposed on opposite sides of said resistance element and parallel thereto, a conductive strip mounted on at least one of said shoulders, a contact member slidably supported on said shoulders and having means engaging the thread of said leadscrcw whereby said contact member is moved lengthwise of said resistance element when the leadscrew is rotated, said contact member making a sliding electrical connection between said resistance element and said conductive strip, and terminal means connected to said conductive strip and to said resistance element.

2. A variable resistor as defined in claim 1, wherein said contact member is provided with at least one portion resiliently spring-pressed against the side of said leadscrew, the outer end of said one portion being serrated so as to form teeth that engage the threads of said leadscrew.

3. A variable resistor as defined in claim 1, wherein said contact member is formed of spring strip metal bent into a U-shaped configuration'and having a flat base portion with upstanding legs at opposite ends thereof, the ends of said legs being serrated to form teeth that engage the thread of said leadscrew, said legs being resiliently urged against the sides of said leadscrew, said flat base portion resting against and sliding on said conductive strip on said shoulders so as to make electrical contact therewith, and a contact finger extending downwardly from said base portion and wiping on said resistance element.

References Cited in the file of this patent UNITED STATES PATENTS 1,728,810 Stickney Sept. 17, 1929 2,439,069 Anderson Apr. 6, 1948 2,638,523 Rubin May 12, 1953 2,761,045 Matthew Aug. 28, 1956 2,777,926 Bourns Jan. 15, 1957 

